Not Applicable
Not Applicable
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1. Field of the Invention
This invention pertains generally to high temperature kiln access door assemblies, and more particularly to a warp resistant supplemental fuel feed door assembly for a rotating kiln.
2. Description of the Background Art
Rotating cylindrical kilns are frequently used in the production of cement. Because such kilns operate at extremely high temperatures, it is possible to burn various forms of liquid and solid combustible waste materials as a source of supplemental heat. Waste materials tend to completely combust at the high operating temperatures found in such kilns, which are on the order of 3400 degrees Fahrenheit and above, while producing little or no undesirable gaseous or solid emissions. Therefore, these waste materials can serve as a form of supplemental fuel, thereby reducing the demand for and cost of the primary fuel.
Worn rubber vehicle tires are particularly suited as a supplemental fuel for a rotary cement kiln. The extremely high temperatures within a cement kiln will cause the rubber tires to burn without any significant liquid, solid or gaseous waste byproducts which might otherwise be detrimental to the environment. Since worn out tires currently present a disposal problem, burning the tires in rotary kilns helps alleviate the growing problem of disposal without impairing the environment.
Various secondary fuel feed mechanisms have been developed to introduce fuel through a kiln wall into the interior of a rotating cylindrical kiln. Typically, these feed systems have an entrance chute which transects the kiln wall with an outer portion protruding through the outer wall of the kiln and an inner portion protruding into the interior of the kiln. The outer portion of the chute normally includes a feed door which opens to allow passage of the secondary fuel into the kiln. Some feed systems positively inject the supplemental fuel into the kiln using a ram or advancing screw mechanism. Other feed systems known tend to use gravity to inject the supplemental fuel into the kiln. A kiln feed door is utilized in both systems to prevent the escape of heat and combustion gases when the supplemental fuel is fed into the interior of the kiln.
The repetitive opening and closing of the kiln feed door results in the exposure of the door to higher temperatures when closed and lower temperatures when open. Such heating and cooling of the door results in expansion and contraction of the door surfaces and warping of the door over time. Warped doors do not properly seal against the entrance chute and allow heat and combustion gases to escape when the door is closed. Replacement of the warped kiln feed door can be costly requiring the kiln to be shut down during the time a new door is installed.
In addition, most door actuating mechanisms are mechanically controlled by the use of cams or rollers and operate within a fixed operating cycle. Such mechanical mechanisms must open the door on each revolution of the kiln and can not skip a cycle. Thus, the rate of secondary fuel introduced into the kiln can not be modified efficiently.
Accordingly, there is a need for a kiln feed door that is resistant to warpage when repetitively exposed to hot and cold temperatures, and which can be opened and closed such that the rate of secondary fuel can be varied. The present invention satisfies those needs, as well as others, and generally overcomes deficiencies found in convention kiln feed door assemblies.
The present invention is a kiln feed door assembly that restricts the loss of heat and combustion gases when feeding tires and other combustible materials into a rotating kiln as a source of supplemental fuel. By way of example, and not of limitation, the apparatus comprises a kiln feed door assembly that preferably includes two feed doors pivotally mounted to a baseplate on the exterior entrance of a chute which transects the wall of the rotary kiln. Each door includes a pivot shaft which preferably pivots within two high temperature pillow block bearings. Preferably four door plate mounting arms are attached to the pivot shaft and extend radially from the center of the pivot shaft. Planar rectangular door plates are mounted to the mounting arms with bolts secured through bores or apertures in the mounting arms.
In the preferred embodiment, there are at least two apertures in each mounting arm. The apertures are matched in pairs in each mounting arm. Some apertures are oblong in shape with the lengthwise portion of the aperture aligned with the direction of the width of the mounting arm. Other oblong apertures are aligned such that the lengthwise portion of the aperture is in the direction of the length of the mounting arm and perpendicular to the length of the pivot shaft. Still other apertures are circular. Each aperture may be sized to receive a bushing.
The bushings and linear alignment of the oblong apertures allow the door plates to expand and contract inconsistently without causing stress or otherwise warping the door. An efficient seal against the loss of heat and combustion products is maintained when the door plates keep their planer shape.
The two kiln doors pivot outwardly from the base plate and center of the kiln. One door assembly has a lip on the outer surface of the door. The lip is positioned to cover and seal the small space between the doors when the doors are in the closed position.
Each kiln feed door of the door assembly is preferably counterbalanced on the pivot shaft, preferably with two counterweights, one disposed near each of the block bearings. The door and counterweights are equally balanced with respect to the pivot shaft allowing for the opening and closing of the doors with little effort.
In one preferred embodiment, the kiln doors synchronously open and close using an electric motor, gearbox, actuating arms, rods and transfer arms. An actuating arm is radially mounted to one end of the pivot shaft of one door and a transfer arm is radially mounted to the other end of the shaft. The actuating arm is connected by an actuating rod to a rotating armature from the gearbox. This portion of the mechanism translates the rotational motion of the armature to oscillating motion of the actuating arm and partial rotation of the pivot shaft. Rotation of the pivot shaft results in movement of the transfer arm. An elongate transfer rod is pivotally connected to the transfer arm on one end and to an arm mounted to the pivot shaft of the opposing door on the other. Therefore, both kiln feed doors open simultaneously when the electric motor is activated.
In one embodiment, the actuating rod that is coupled with the door actuating arm on one end and the rotating linkage of the gearbox on the other includes a dampening member which tempers the impact of the closure of the doors against the rim of the opening to the kiln thereby reducing stress on the doors and linkage.
In another embodiment, the activity of the motor is regulated during various times of the cycle of the rotation of the gearbox armature with sensors thereby regulating the rate of movement of the door-actuating rod. When the motor is momentarily turned off just before the doors are fully closed or opened, the stress on the seals, doors and linkage of impact against the kiln opening under power is eliminated.
In operation, tires or other combustible materials are presented to a feed ramp or injection platform. As the kiln rotates, the feed door assembly eventually comes into proper alignment with the feed ramp. The kiln feed doors are mechanically or preferably electrically opened to allow the kiln to receive the combustible materials from the ramp. The doors are closed after the combustible material enters into the kiln to eliminate the loss of heat and combustion products from the kiln during rotation.
An object of the invention is to provide secondary fuel access doors for a rotating kiln that can expand linearly or laterally without warping.
Another object of the invention is to provide kiln feed doors that will efficiently prevent the escape of heat and combustion products from the interior of the kiln yet allow the efficient entry of tires or other combustible material into the kiln.
Another object of the invention is to provide a kiln feed door that can be repetitively exposed to heat extremes and cooling and maintain its shape.
Yet another object of the invention is to provide a door actuating mechanism that efficiently and reliably allows momentary access to the interior of the kiln without releasing large amounts of heat or combustion gases.
Still another object of the present invention is to provide a kiln supplemental fuel feed door assembly that can be programmed to open and close at desired times and is capable of skipping cycles.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.